1Pnmpsnr User Manual(0) Pnmpsnr User Manual(0)
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6 pnmpsnr - compute the difference between two images (the PSNR)
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10 pnmpsnr
11 [pnmfile1]
13 [pnmfile2]
15 [-rgb] [-machine] [-max=n] [-target=n] [-target1=n] [-target2=n] [-tar‐
17 get3=n]
18 Minimum unique abbreviations of options are acceptable. You may use
20 double hyphens instead of single hyphen to denote options. You may use
21 white space in place of the equals sign to separate an option name from
22 its value.
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27 This program is part of Netpbm(1).
28 pnmpsnr reads two PBM, PGM, or PPM files, or PAM equivalents, as input
30 and computes the magnitude of difference between the two images as a
31 peak signal-to-noise ratio (PSNR) This metric is typically used in
32 image compression papers to rate the distortion between original and
33 decoded image.
34 pnmpsnr either prints these values or compares them to thresholds you
36 specify.
37 The PSNR of a given component is the ratio of the maximum mean square
40 difference of component values that could exist between the two images
41 (a measure of the information content in an image) to the actual mean
42 square difference for the two subject images. It is expressed as a
43 decibel value.
44 The mean square difference of a component for two images is the mean
46 square difference of the component value, comparing each pixel with the
47 pixel in the same position of the other image. For the purposes of
48 this computation, components are normalized to the scale [0..1].
49 The maximum mean square difference is identically 1.
51 So the higher the PSNR, the closer the images are. A luminance PSNR of
53 20 means the mean square difference of the luminances of the pixels is
54 100 times less than the maximum possible difference, i.e. 0.01.
55 Note that the word "peak" is a misnomer; there is no maximum involved;
57 the metric is a mean. But "peak signal to noise ratio" is for some
58 reason the common term for this measurement.
59 If the inputs are PBM or PGM, pnmpsnr computes the PSNR of the lumi‐
61 nance only. Otherwise, it computes three separate PSNRs: either the
62 luminance, and chrominance (Cb and Cr) components of the colors or the
63 red, green, and blue components.
64 By default, the program prints the PSNRs to Standard Output in human-
66 friendly form.
67 With the -machine option, the program prints the PSNRs, but in machine-
69 friendly form.
70 With a -target[x] option, the program just prints 'match' or 'nomatch',
72 depending on whether the PSNRs exceed targets you specify.
73 pnmpsnr reports the PSNR either in human-friendly form or in machine-
76 friendly form (see -machine).
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81 -rgb This option causes pnmpsnr to compare the red, green, and blue
82 components of the color rather than the luminance and chromi‐
83 nance components. It has no effect on a monotone image.
84 This option was new in Netpbm 10.71 (June 2015).
86 -machine
89 This option causes pnmpsnr to report the PSNRs in machine-
90 friendly form, so another program can easily use the informa‐
91 tion.
92 The output is a single line. It contains one floating point
94 decimal number for each color component, with a single space
95 between every two. (This means there are either 1 or 3 num‐
96 bers). For the YCbCr color space (no -rgb), they are in the
97 order Y, Cb, Cr. For the RGB color space (-rgb), they are in R,
98 G, B order. For a monotone image, there is one number.
99 Where the component does not differ between the images, so the
101 PSNR is infinite, the number is inf
102 But note that the number displayed is also modified by the
104 effect of -max. In particular, with -max, you will never see
105 inf.
106 This option has no effect when you also specify -target[n].
108 This option was new in Netpbm 10.74 (March 2016).
110 -max=n This is meaningful only with -machine.
113 It specifies the maximum number pnmpsnr will print as a PSNR.
115 If the PSNR is greater than n, pnmpsnr just prints n. n is a
116 decimal floating point number. An infinite PSNR is considered
117 greater than any number.
118 This is mainly useful to deal with infinite PSNRs. It is often
120 much more convenient to have a program process only numbers than
121 to make it deal with infinity, and often a very large number has
122 the same effect on a program as infinity.
123 Note that the output is logarithmic, which means you will not
125 see really large but finite numbers. If you specify -max=1000,
126 the only way you will see 1000 in the output is if the PSNR is
127 really infinite. Two images with as many pixels as there are
128 electrons in the universe, differing in only one pixel, and only
129 in the smallest amount representable in the Netpbm format, have
130 a PSNR less than 1000.
131 This option was new in Netpbm 10.74 (March 2016).
133 -target=n
136 This option causes pnmpsnr to run in comparison mode - rather
138 than print the PSNRs, it just tells you whether the PSNRs exceed
139 n (a floating point number), i.e. whether the compared images
140 are the same within a given margin of error. If all the com‐
141 puted PSNRs (luminance for a PBM or PGM; luminance and chromi‐
142 nance or red, green, and blue for PPM) exceed n, the program
143 prints 'match' to Standard Output. Otherwise, it prints
144 'nomatch'.
145 If you also specify any of -target1, -target2, or -target3, and
147 the images are color, pnmpsnr ignores -target.
148 This is mainly useful for use in a program. If you're running
150 pnmpsnr manually, you could just run pnmpsnr without -target and
151 compare the PSNRs to your targets yourself.
152 This option was new in Netpbm 10.82 (March 2018).
154 -target{1,2,3}=n
157 Like -target, these options cause pnmpsnr to run in comparison
158 mode. But they provide separate targets for the individual
159 color component PSNRs. -target1, target-2, and -target3 are for
160 either the Y, Cb, and Cr components, respectively, or the red,
161 green, and blue components, respectively, depending upon whether
162 you specified -rgb.
163 If you don't specify the corresponding -targetn option for a
165 component, pnmpsnr ignores the PSNR of that component in decid‐
166 ing whether the images match.
167 If the image is a PBM or PGM, these options have no effect,
169 except that it stilll selects comparison mode, so if you don't
170 also specify -target, and the image is PBM or PGM, the program
171 fails.
172 Note that the options are defined so that you could code a pnmp‐
174 snr command in a program that works on both color and monotone
175 images, specifying individual PSNR targets for use on the color
176 images and the single target for use on the monotone images.
177 These options were new in Netpbm 10.82 (March 2018).
179
185 pnm(1)
186
188 This manual page was generated by the Netpbm tool 'makeman' from HTML
189 source. The master documentation is at
190 http://netpbm.sourceforge.net/doc/pnmpsnr.html
192netpbm documentation 06 January 2018 Pnmpsnr User Manual(0)